Method of mixing bituminous materials with fillers



Jan.- 189, 1949. B. D. GREENSHIELDS 2,459,520

METHOD 6F MIXING BITUMINOUS- MATERIALS wI'lH FILLERs Filed Aug. 22, 1&44

5b :inventor B @mf attorney i This invention relates Patented Jan. 18, 1949 UNITED sTAT'ss PATENT OFFICE` N `METHOD oF MIXING BITUMINoUs MATERIALS WITH FILLERS Bruce D. Greenshields, New York, N. Y.

Application August 22, 1944, SerialNo. 550,656 4 claims. (c1. 10e-283) `material to secure increased stability of the `mixture when it is used as a paving material. A further advantage of my method is that it perimits the use of softer asphalts `which are less subject to temperature changes and tooxidation.

Still another advantage of my method is that it produces a bituminous mixture ina loose granular state Whichmay be easily handled and stored cold and which maybe laid and compacted into a dense, stable pavement by the application of pressure withoutheat. The mixture resulting from my process may also be used in the making of pavements by the hot-laid method.`

Finally, the product of my improvedmethod possesses certain advantages in mixing with a coarser aggregate, especially is heated during mixing.

Various methods have been used in the pastfor mixing fine fillers `with asphalt. The most common method has been to liquefy the bitumen by heat and then stir in the fillers by a pug-mill, but this method is not entirely satisfactory because the mixture is'not entirely homogeneous and fatty spots develop in the pavement. Furthermore, the mixture is not easily handled.

Another commonly used method is `to mix the filler with a bituminous emulsion or cut-back.

Where the mixture `This method is not entirely satisfactory because of the added cost due to the fact that the emulsion contains water and the cut-back a solvent which `arenot binders but which add to the cost and must be paid for.

Still another `method employed for mixing bituminous materials and llers involves atom izing `hot bitumen into a cloud,` and simultaneousiy spraying the finely divided dry nner into the cloud `Where the filler `particles become intimately mixed With bitumen particles, the mix ture being in the formofdust. This method is not entirely satisfactory because it is rather critical as to temperature and moisture conditions during processsing, and 1t is difficult to secure a mixture which contains enough soft bitumen to form a good stable pavement and Whichvvll not coalesce in Warm Weather. o

My method of mixing `overcomes many of the difficulties found in priormethods and produces almixture which contains adequate bitumenfor pavement use. Furthermore, the `product of my method may be easily handled and it vforms a highly stable pavement.

vAccording to my invention, the bituminous material or other binder is` iirst liquefied byheat and then is atomized or sprayed into `a cloud.

`The fine filler material is mixed with Water and formed into a slurry, and then the slurry is atomized. or sprayed into a cloud which mingles with the bituminous cloud where the particles 'of slurry `become coated with particles of bitumen.

The coated particles are then collected and used for the formation of paving material in almann'er to be described hereinafter.

One example of suitable apparatus for carrying out my` improved method is illustrated in the accompanying drawingin which p Figure l is a diagrammatic View of mixing apparatus with a mixing lchamber beingjshown in vertical section; Figure 2 is a sectional view` of `an atomizer; and Y Figure 3 is an end view of one of the parts of the atomizer. p o p f Referring to the drawing, I indicates a mixing chamber which preferably isinlthe form of a vertical cylinder, the upper end of which may `be either open or closed. The lower endof the chamber `I is provided with a conical portion la having a discharge opening in the bottom `thereof. Mounted in the` center of the chamber l l,is a rotary shaft `2 which extends out of the upper end Aof the chamber and is provided witha pulley 2a which is driven from any suitable sourcerepresented by the motor M. The shaft 2 carries `an upper setof radial arms 2b ,andra lower set of arms 2c to the ends of whichare secured a series of Vertical scraper vanes 2d. As will be seen in Figure 1, eachvane Zdisformed of a straight vertical section which engages the cylindrical Aportion of the mixing chamber and an inclined l or spraying device 5tthrough `connection 4b.

Slurry from tank 3 is supplied to a second atomizer 8 through connection 3a`. `Compressed air is supplied to atomizer `6 from` a suitable source through pipeline T. Compressed air is also supplied to atomizer 5 through a suitable supply line 8, and the air supplied to this atomizer is heated by suitable means represented by the heating coil 9 interposed in the line 8 and heated by a suitable heater Ill. II is a device which responds to the temperature of the air supplied to atomizer 5 and controls the fuel supply valve I2 in the supply line of burner I0 through connection I2a to maintain the air at a predetermined temperature.

Atomizing devices 5 and 6 are arranged on the outside of mixing chamber I and have their discharge ends directed into an opening Ib formed in the wall of the chamber. The two atomizers are arranged in angular position to direct an atomized cloud or fog of bitumen into the mixing chamber and also an atomized cloud or fog of slurry into the same space within the chamber.

Various known constructions of atomizers` may Ibe employed, and one suitable construction is illustrated in Figures 2 and 3.

'Referring to Figure 2, the atomizing device is formed of an outer casing 5 which has an internal bore threaded at the rear' end and is provided with a conical shaped discharge opening 5a at the front end thereof. 'Compressed air is supplied to the bore of the housing 5 through a pipe coupling 5b. A sleeve 5c having a nut portion 5c at the rear end thereof is threaded inthe rear end of housing 5 and extends towards the front of the bore in the housing. vAn inner nozzle 5d having 'a conical outer surface at the front end is supported within sleeve 5c and has its forward end positioned within the conical nozzle 5a of housz-r.'

ing 5 in the manner-shown in Figure 2. The rear 4end of the nozzle 5d is provided with a pipe coupling through which the fluid to be atomized is supplied. For the purpose of giving the spray a swirling action, the front end of sleeve 5c is slotted at two or more places as shown at 5c, and these slots are arranged at an angle to the radius of the sleeve as shown' in-Figure 3. By this cony struction, the streams of air' owing through the slots 5e are given rotary or swirling action as Vshown by theV arrows in Figure 3, and this swirling action continues after the spray leaves the atomizing device and tends to spread out or disperse the' cloud or fog.

, My improved method is carried out/,as follows: The Aiinely divided nller material, such as stone dust, clay, Portland cement, or finely divided 'iibers of wood, asbestosor the like, is rst mixed with water to form a slurry, and this mayl be accomplished by mixing in an ordinary pug-mill. The slurry thus formed is supplied to container 3 either continuously or in batches. The asphalt or other bituminous material is maintained in a .liquid state in container 4 by means of burner 4a `become coated `with particles of atomized bitumen, and the coated particles either adhere to the wall of the mixing chamber or drop downand pass out through the discharge opening at the lower end thereof. Any particles which adhere to the walls of the mixing chamber are scraped off by i scraper vanes 2d and fall by gravity and pass through the'discharge opening.` The mixed product passing through the discharge opening at the lower end of the mixing chamber consists of mineral iines and tar or asphalt and water. This mixture is a wet mass which may or may not be sticky depending upon the amount of water used. Preferably enough water is used to prevent the mass from being sticky, and this greatly facilitates the handling of the mixture.

In carrying out the method the asphalt or other binder should be heated to a temperature high enough to liquefy it, but not so high as to cause burning.V Depending on the hardness of the bitumen, the temperature will vary from about 250 to 375 F. In case of gilsonite which liquefles at 375 F., the temperature is rather critical ii burning is to be avoided. The temperature of the air supplied to the bitumen atomizer should be of the order of 250 F. or higher. The temperature of the slurry is not critical and may be the same as room temperature or the temperature of the available source of water` and under ordinary conditions the temperature of the slurry would range from about 50 F. to about 90 F.

The mixture discharged from the mixing chamber I passes into a conduit I3 by which the mass may be conveyed or conducted to storage or to a pug-mill where the coarser aggregates may be added for the purpose of making a pavement mixture.

' The wet mass which is discharged from-mixing chamber I may be easily handled, since the particles do not coalesce. The presence of the entrained water apparently prevents the particles from coalescin'g. At the same time, on drying, the cohesive action of the water on the mineral particles tends to draw the mass together and to squeeze the asphalt or bitumen and thus cause it to ilow around and coat the mineral particles. It seems likely ythat the asphalt does not have actual contact with the particle until the water is forced out by pressure or is evaporated, either naturally or by heating.

For the'purpose of withdrawing excess air from the mixing chamber,` I provide an exhaust fan I4 having its inlet connected with the lower end of the 'chamber at I 4a, and its outlet leading to a dust collector such as bag I5. This feature. is not necessary unless a dry mixture is to be produced.

The wet mass obtained from the mixing chamber I may be incorporated in road material by mixing the mass with coarser aggregrate such as sand and gravel, and the mixing may be either in the cold state by adding a small amount of water, or the mixing may be facilitated by the application of heat to the mixture. Where heat is used, the mixture is heat-ed to convert `the water into steam which disperses the material and makes it easy for the mass to mix with the coarser aggregate. This method of mixing is quite eiective, sincesteam is produced around each fine particle of the wet mass where it is most effective, it being remembered that the iine particles cause most of the difficulty in mixing. If it is desired to produce a hot-laid mixture, all or nearly all of the water should be driven on during mixing of the coarser aggregate, and if a cold-laid mixture is to be produced, a small percentage of the water should be left in the mixture to prevent coalescing.-

While I have described my process as applied to bituminous materials, it is obvious that other bindery materials may be used instead of or in addition to bituminous materials, such as resinous substances, either natural or synthetic. Also,

the liquefied binder may be atomized by other types of devices than the air spray disclosed herein, such as by a pressure spray.

It will be obvious that other forms of apparatus may be devised for carrying out my improved process.

I claim:

1. The method of mixing bituminous material with nely divided ller which consists in forming a water slurry of the ller material, atomizing the slurry into a cloud, heating the bituminous material to liquefy the same, atomizing the liquid bitumen by an air spray heated to a temperature of the order of 250 F., and introducing a cloud of said atomized bitumen into the same space With the atomized slurry cloud.

2. The method of forming a non-coalescing mixture of bitumen and finely divided ller material which consists in forming a, water slurry of the filler material at room temperature, atomizing the slurry into a cloud, heating the bitumen to liquefy the same, atomizing the liquid bitumen by a spray of air heated to a temperature of the order of 250 F., and introducing a cloud of said atomized bitumen into the same space with the atomized slurry.

3. The method of forming a paving mixture which consists in forming a Water slurry of finely divided ller material, forming an atomized cloud of said slurry, forming an atomized cloud of bituminous material in the same space with the cloud of slurry, collecting the wet mass of particles deposited from said clouds, and mixing 3U Number said mass with coarser aggregate while heating the same to a temperature above the boiling point of Water.

4. The method of mixing bituminous materials with inely divided filler which consists in forming a water slurry of the filler material at a temperature less than F., atomizing the slurry into a cloud, heating the bituminous material to liquefy the same, atomizing the liquid bituminous material by an air spray heated to a temperature of the order of 250 F., and introducing a cloud of said atomized bituminous material into the same space with the atomized slurry cloud.

BRUCE D. GREENSHIELDS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Downard Sept. 3, 1929 Downard Nov. L11, 1930 Brito Apr. 12, 1932 Sommer Sept. `22, 1936 Sommer Aug. 2, 1938 Sommer Mar. 27, 1945 FOREIGN PATENTS Country Date Great Britain Aug. 24, 1937 Australia 1929 Number 

